Let's describe the general attributes and behavior of any Person.
A Person can **walk**, given a specific distance. This is described as
follows: its distance will be its distance plus what we previously defined as
`distance`. Finally we return its hunger will be its hunger plus the number
2..
A Person can **eat**, given a specific food. This is described as follows:
Finally we return its hunger will be its hunger minus the result of calling
**nutritional_value** on what we previously defined as `food`..
And with this we're done describing a Person.